does the rehab where he is at have family sessions? you certainly are not the first to have these questions which are very valid.
They say it takes a good year for the drugs to get removed from the brain and for normal blood flow to get going into the frontal cortex which is the part of the brain your son needs to address his social issues. Having said that, they are his social issues, and he is in the right place right now to address them and get good advice - not from you mom (sorry) but from the environment he is in.
So I would suggest going to the family sessions at your son's rehab. Even if he has not signed a medical consent for you to be in on his therapy, you can still go to the sessions and ask your questions. I think you'll be glad you did. They can continue to remind you of where your son's brain is at in this stage of his recovery and what you can say or not say that will not be a source of hurt but a source of healing for your son.
Remember, don't focus on the problem - focus on the solution! That is what your son has to do, and if he can do it, so can you!